The present invention generally relates to a vacuum heat treatment method (such as, sputtering, vapor deposition, or etching) for processing an object to be processed in a vacuum ambience while heating the object to be processed, and in particular, to a technique for heating an object to be processed with a heating lamp.
Objects to be processed (such as, semiconductor wafers or liquid-crystal glass substrates) have been processed by sputtering or vapor deposition so as to form thin films thereon or to pattern thin films on the object to be processed by etching or the like.
When such a processing is performed, the objects to be processed are heated for vacuum heat treatment, and employed as heating devices are resistive heaters that generate heat when energized or alternatively heating lamps that allow object to be processed which is located apart from the heating lamps.
The heating lamp, which heats an object to be processed mostly by radiation in a vacuum of a low thermal conductivity, so that the heating lamp requires a high electric current and is thus supplied with low-voltage power converted from a high-voltage three-phase AC power source. In a vacuum chamber, the reduced low voltage may advantageously provide a reduced potential difference between a voltage applied portion and the grounded chamber wall of the vacuum chamber, thereby causing no discharge in the presence of a potential difference of 100 V or less.
The heating lamp, a given number of which are included in one load, is supplied with power from one secondary winding of a three-phase transformer. Because the three-phase AC power source has three secondary windings, it may lead to a three-phase transformer having an unloaded secondary winding when the number of loads is other than a multiple of three. This may cause the three-phase AC power source to supply an unbalanced current from each phase and to be degraded in service efficiency, thereby requiring a large-capacity three-phase transformer.
See, [Patent Document 1] Japanese Patent Application Laid-Open No. Hei 10-294285, and [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-190452.